The present invention relates to an automotive alternator, and particularly to a Lundell-type core construction of an automotive alternator enabling claw resonance noise generated by magnetic attraction force force acting on claw-shaped magnetic poles to be reduced by improving the magnetic balance of magnetic attraction force.
In recent years, due to noise reduction in engines and the accompanying reduction of sound insulation equipment, the lowering of noise in automotive alternators mounted to the engines is in demand. Noise in automotive alternators can be classified roughly into two groups including wind noise generated by fans and electromagnetic noise, and higher harmonic electromagnetic noise is particularly a problem, being harsh in tone.
Generally, it is known that magnetic attraction force proportional to rotational frequency is generated in automotive alternators in air-gap portions between claw-shaped magnetic pole portions of a field rotor and teeth of a laminated core of a stator, electromagnetic noise being generated by component parts resonating at their excitation frequencies. It is difficult to avoid resonance in component parts in automotive alternators because the working rotational frequency range is spread over 1,000 to 20,000 revolutions per minute (rpm). In a field rotor, in which the resonating frequency is comparatively high, the claw-shaped magnetic pole portions resonate in the vicinity of 9,000 rpm. Because the noise level of this electromagnetic noise is affected by the magnitude of the vibrational amplitude, it is important to suppress vibrations to reduce electromagnetic noise.
Thus, attempts have been made conventionally to reduce electromagnetic noise by engaging a vibration-suppressing ring in an interior portion of the claw-shaped magnetic pole portions to shift the resonating frequency of the claw-shaped magnetic pole portions to a frequency band higher than the working rotational frequency range, or to reduce electromagnetic noise by applying a resin to the claw-shaped magnetic pole portions to dampen vibration of the claw-shaped magnetic pole portions.
However, from the viewpoint of improving output, automotive alternators of this kind are generally designed such that the axial length of the laminated core of the stator is shorter than the axial length of the claw-shaped magnetic pole portions, and the outer radius of cylindrical portions is smaller than the outer radius of the field rotor, structurally making for constructions which vibrate easily. Thus, since magnetic attraction force is concentrated at tip portions of the claw-shaped magnetic pole portions and the vibrational amplitude in the radial direction increases, and in addition, the distance from the cylindrical portions to the claw-shaped magnetic pole portions is great, vibrational amplitude in an axial direction resulting from magnetic attraction force is increased, preventing electromagnetic noise from being reduced effectively even if the countermeasures described above are applied.
An attempt is proposed in Japanese Patent Laid-Open No. HEI 11-164499, for example, to try to achieve high output by making the laminated core of the stator and the yoke portions of the field rotor face each other to minimize the magnetic flux leaking outside from the yoke portions and thereby increase the rate of recovery of the magnetic flux generated by the field rotor.
In Japanese Patent Non-Examined Laid-Open No. HEI 11-164499, as shown in FIG. 14, it is stated that high output can be achieved by setting a ratio between an axial length L1 of a laminated core 51 of a stator and an axial length L2 of cylindrical portions 52a of a Lundell-type core 52 to a range from 1.25 to 1.75 and setting a ratio between an outer radius R1 of the Lundell-type core 52 and an outer radius R2 of the cylindrical portions 52a to a range from 0.54 to 0.60.
However, no comment has been made in Japanese Patent Non-Examined Laid-Open No. HEI 11-164499 about reducing electromagnetic noise resulting from vibration of the claw-shaped magnetic pole portions.
An object of the present invention is to provide an automotive alternator achieving high output by overlapping a laminated core of a stator and yoke portions of a field rotor in an axial direction, and enabling electromagnetic noise to be reduced by prescribing dimensional relationships in the field rotor.
According to one aspect of the present invention, there is provided an automotive alternator including:
a field rotor provided with:
a field coil; and
a Lundell-type core having:
a cylindrical portion on which the field coil is installed;
yoke portions disposed so as to extend radially outward from axial end portions of the cylindrical portion; and
claw-shaped magnetic pole portions disposed so as to extend axially from radial edge portions of the yoke portions so as to surround the field coil; and
a stator composed of a laminated core and an armature coil disposed facing an outer circumference of the claw-shaped magnetic pole portions,
wherein a ratio (R2/R1) between an outer radius R2 of the cylindrical portion and an outer radius R1 of the Lundell-type core is in a range from 0.50 to 0.54, and
a ratio (Tr/Tp) between an axial overlap length Tr between the laminated core and the yoke portions and an axial length Tp of the yoke portions is in a range greater than or equal to 0.2.
According to another aspect of the present invention, there is provided an automotive alternator including:
a field rotor provided with:
a field coil; and
a Lundell-type core having:
a cylindrical portion on which the field coil is installed;
yoke portions disposed so as to extend radially outward from axial end portions of the cylindrical portion; and
claw-shaped magnetic pole portions disposed so as to extend axially from radial edge portions of the yoke portions so as to surround the field coil; and
a stator composed of a laminated core and an armature coil disposed facing an outer circumference of the claw-shaped magnetic pole portions,
wherein a ratio (Tt/R1) between a radial dimension Tt of a root portion of the claw-shaped magnetic pole portions and an outer radius R1 of the Lundell-type core is in a range from 0.1 to 0.15, and
a ratio (Tr/Tp) between an axial overlap length Tr between the laminated core and the yoke portions and an axial length Tp of the yoke portions is in a range greater than or equal to 0.2.
According to yet another aspect of the present invention, there is provided an automotive alternator including:
a field rotor provided with:
a field coil; and
a Lundell-type core having:
a cylindrical portion on which the field coil is installed;
yoke portions disposed so as to extend radially outward from axial end portions of the cylindrical portion; and
claw-shaped magnetic pole portions disposed so as to extend axially from radial edge portions of the yoke portions so as to surround the field coil; and
a stator composed of a laminated core and an armature coil disposed facing an outer circumference of the claw-shaped magnetic pole portions,
wherein a ratio (R3/R1) between a bottom portion outer radius R3 of a valley portion between the daw-shaped magnetic pole portions and an outer radius RI of the Lundell-type core is in a range from 0.55 to 0.65, and
a ratio (Tr/Tp) between an axial overlap length Tr between the laminated core and the yoke portions and an axial length Tp of the yoke portions being in a range greater than or equal to 0.2.